In a number of clinical applications, X-ray apparatuses which include an X-ray source and X-ray detector mounted to a rotational arm are common. These systems provide the ability to rotate the X-ray source and detector to varying angles to obtain images without requiring the patient to move. A mammography system, for example, typically comprises an X-ray source, an X-ray detector, a breast support plate, and a breast compression plate. The source and detector are mounted to opposing ends of an arm, such as a C-arm, and the arm is disposed to rotate around the breast support and compression plates. The breast is positioned between the breast support and breast compression plates to hold the breast in place during mammography, and is arranged between the source and the receiver on the opposing ends of the C-arm. During mammography, the C-arm is rotated about the breast plates such that images of the breasts are acquired from varying angles.
For construction reasons, and due to the varying weights of the components, the center of mass of the rotatable C-arm is typically spaced apart from the axis of rotation, and is therefore “unbalanced” about the axis of lateral rotation. In an unbalanced system, a significant torsional force must be applied to rotate the arm to a desired position. It is desirable, however, to reduce the amount of force required to rotate the arm, to simplify use of the equipment for medical personnel.
To balance the system, counterweights are typically used to provide a counteractive torsional force. While counterweights significantly reduce the torsional force that must be applied when rotating the arm, they add significantly to both the weight and cost of the system. Furthermore, the counterweights make it very difficult to move the mammography system from place to place when desired. It is desirable, therefore, to provide alternate methods for balancing a mammography or other imaging system comprising an arm in which the torsional force required for rotation is reduced.